Erythromycin A is an antibiotic clinically widely used as an agent for treating infectious diseases caused by Gram-positive bacteria, mycoplasmas, etc. However, erythromycin A is decomposed by the gastric acid due to instability to acids, and thus have a drawback of no constancy of movement in the body. Hitherto many erythromycin A derivatives have been prepared for the purpose of the improvement of the biological or pharmacological properties. For example, it is reported that 6-O-methylerythromycin A derivatives have an improved stability to acids and have a superior in vivo antibacterial activity in comparison with erythromycin A when administered orally (U.S. Pat. No. 4,331,803). There are also recent reports relating to 11,12-cyclic carbamate derivatives prepared from 6-O-methylerythromycin A as a starting material with the aim of expansion of antibacterial spectrum as well as a stability to acids (EP. patent No. 487411 and U.S. Pat. No. 4,742,049). In addition, the present inventors refer to the antibacterial activity of the ester derivatives at the 3-position (EP. Patent No. 619320).
An object of the present invention is to provide a novel antibiotic erythromycin A derivative or a salt thereof having a strong antibacterial activity against not only known erythromycin-sensitive bacteria but also erythromycin-resistant bacteria which recently are showing a tendency to increase, and a composition comprising the same as an effective component.
Other objects of the present invention are to provide a method for the treatment of a bacterially infectious disease which comprises administering a pharmaceutically effective amount of the above-mentioned erythromycin A derivative or a salt thereof to patients, and use of the above-mentioned erythromycin A derivative or a salt thereof for the treatment of a bacterially infectious disease.